Space discharge tube



-Ma -1s, 1937.

' E. F. CARTER SPACE DISCHARGE TUBE Filed Jan. 8, 1934 ATTORNEY Patented May 18, 1937 UNITED STATES PATENT OFFICE SPACE DISCHARGE TUBE Emmett Finley Carter, Emporium, Pa., assignor to Hygrade Sylvania Corporation,

Salem,

12 Claims.

This invention relates to wave transmission systems and with particularity to methods and apparatus for transmitting and receiving modulated waves.

An object of the invention is to provide a novel form of discharge tube which is capable of acting as an oscillator-modulator, oscillator-demodulator or oscillator-detector.

Another object of the invention is to provide a novel method of eiiecting series modulation.

Another object is to provide a method of modulating the electron stream of a space discharge tube without affecting the input circuit of said tube by the local oscillations.

A feature of the invention relates to an improved form of space discharge tube capable of acting as an oscillator-modulator, oscillator-demodulator or oscillator-detector.

Another feature relates to an improved form of detector tube for modulated carrier waves or the like.

A further feature pertains to a space discharge tube having a pentode section, and a spacecharge triode section with one or more electrodes common to both sections.

A further feature relates to a space-charge tube having a pentode section and a triode section, wherein the same electrode serves as the control grid for the triode section and as a suppressor grid for the pentode section.

A further feature relates to a space discharge tube having a modulator section and an oscillator section wherein the shield grid of the modulator section also serves as a space-charge grid 'for the oscillator section.

A still further feature relates to the improved arrangement, relative location and connection of parts which go to make up a relatively simple and stable oscillator-modulator, oscillator-demodulator or oscillator-detector system.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed description and the appended claims. 7

While the invention will be disclosed herein as embodied in specific structures and circuit arrangements, it will be understood that this is done merely for purposes of explanation and not by way of limitation.

Accordingly, Fig. 1 of the drawing shows a schematic circuit diagram embodying a tube and circuit features of the invention;

Fig. 2 is a detailed structural view of the tube schematically illustrated in Fig. 1.

Referring more particularly to Fig. 1 of the drawing, the numeral I indicates an evacuated envelope containing the novel electrode system. This system comprises in general a cathode preferably, although not necessarily, of the thermionic emitting type. As shown, the cathode may be of the so-called indirectly heated type comprising an electron emitting coating 2 carried by a suitable metal sleeve 3. Insulatingly mounted within the sleeve is a heater member or filament 4 of any well-known construction. It will be understood, of course, that the invention is not limited to an indirectly heated cathode, and therefore a so-called filamentary cathode may be employed. Surrounding the cathode are two electrode systems, namely, an upper modulator system preferably, although not necessarily, of the pentode type: and a lower or oscillator system preferably, although not necessarily, ofthe triode type. The upper system comprises in addition to the cathode 2, a foraminous control grid 5, a foraminous inner screen or shield grid 6, a foraminous suppressor grid 1, a plate or anode 8, and an outer'screen or shield grid 9 electrically connected to the inner shield grid 6.

As will be seen from the drawing,the electrodes 6 and I are substantially coextensive in length with cathode 2, while electrodes 8 and 9 are materially shorter than the said cathode. Surrounding the lower end of cathode 2 and. electrodes 6 and 1 is a plate or anode l which is preferably separated from anode 9 by an insulator disc or ring II. The various electrodes may be mounted in any well-known manner, preferably concentrically as shown schematically in Fig. 1 and as shown in detail in Fig. 2, described hereinbelow. While the electrodes 5, 6, l and 8 are schematically illustrated in the form of meshwork, it will be understood that any well-known form of grid construction as employed in radio tubes may be employed.

When the device is to be used in a system for receiving modulated waves, these waves are impressed across the cathode 2 and the grid in the customary manner, for example, by means of an input transformer of which the secondary winding I2 is connected at one end to the grid 5 and at the other end through condenser I3, thence through grid-biasing resistance M to the cathode 2. In accordance with standard practice, the bias resistor l 4'is shunted by a suitable condenser l5. Preferably also, the input circuit comprises a tuning condenser I 6, it being understood that any other form of tunable or tuned signal input circuit may be employed. The signal output circuit includes, for example, the primary I! of a coupling transformer having one terminal connected to anode 8, and the other terminal connected to the positive terminal |8 of a suitable source of anode potential. The signal output circuit may be tuned by means of a variable condenser l9, and also, if desired, the secondary of transformer may likewise be tuned by variable condenser 20. The filament 4 may be heated from any customary source, for example, from the secondary of a step-down transformer 2|. The screen grid 6 of the upper or pentode section of the device I, is maintained at a suitable steady potential preferably less than the potential of anode 8, by connecting said grid to the positive terminal l8 through a series resistance 22. Preferably, the

screen grid is connected to ground through a high resistance 23 and a shunt condenser 24. The pentode suppressor grid instead of being connected to the source of potential through a resistor or the like, is connected to the terminal |8 through the space between the anode I0 and the lower section of the cathode. In other words, the potential of the suppressor grid varies in accordance with the variations in space current between anode HI and the associated cathode section. The operating potential for anode I0 is supplied through a suitable resistor, while the lower end of grid 6 has a positive potential applied thereto through resistance 22, as above described. Preferably, the potential of gridt is chosen so as to cause its upper portion to act efiiciently as a screen or shield grid for the pentode section of the device, while its lower portion acts as a space charge grid for the lower or triode section. When the device I is to be used as a detector-oscillator, the anode I0 is connected through a suitable regenerative or feed-back circuit to the associated grid, the lower section of which therefore acts as a control grid between anode I8 and the lower section of the cathode 2. Thus, as shown in the drawing, anode H3 is connected throughfeed-back inductance 26 and stopping condenser 21, resistances 28 and M, to cathode 2. This latter circuit constitutes, therefore, the oscillating output circuit for the lower or triode section. The grid or input circuit of the triode section may be traced from grid conductor 29, inductance 39, thence through resistances 28 and |3, to cathode 2.

As shown in the drawing, inductances 28 and 30 are placed in inductive or feed-back relation, and preferably the grid circuit is tunable by a variable condenser 3, to the desired frequency of oscillations to be generated. By means of the lower triode section and feed-back circuit described, there are generated sustained oscillations whose frequency may be. varied by condenser 3| in known manner. Consequently, the potential of grid T will vary in accordance with the oscillations generated in the triode section. Since the upper section of grid 1 is interposed in the path of the electron stream between cathode 2 and anode 8, a corresponding modulation of the latter stream is eifected. Consequently, if a modulated carrier wave is impressed upon the signal input circuit and therefore upon grid 5, there will appear in the signal output circuit a correspondingly modulated wave having a frequency determined by the above-described feed-back circuit, it being understood that the signal output circuit is tuned to the frequency of this latter wave, These modulations in the signal output circuit may be passed to a succeeding stage or stages, such as a detector stage, an amplifier stage, or the like. If desired, the oscillations generated in the triode section as described may be chosen of such a frequency with.

relation to the frequency of the waves impressed upon the signal input circuit, as to cause the modulations in the impressed carrier to be detected by the well-known heterodyne or homodyne methods. Or the arrangement disclosed may be used to modulate a received carrier wave by the locally generated oscillations to convert the received modulated waves into a correspondingly modulated wave of lower or higher frequency, for example, an intermediate frequency such as ordinarily employed in so-called superheterodyne circuits. Thus the device may be used to detect by heterodyning the local oscillations with the impressed carrier oscillations. In any event, the

above-described arrangement has the decided ad vantage that since the local oscillations are impressed upon the pentode suppressor grid 7, and since this grid is electrostatically shielded from the signal input circuit by shield grid 6, the oscillations are substantially entirely isolated from the said input circuit. Thus, if the input circuit shown is connected to a receiving antenna or the like, there is substantially negligible coupling between the local oscillator and said antenna. It has been found that this arrangement gives satisfactory performance with a translating gain from received to intermediate frequency of the order of to 120, and the frequency characteristic is very stable and is substantially imperceptibly affected by a wide variation of signal voltage impressed upon control grid 5. Ifdesired, grid 5 may be wound exponentially, i. e., with a varying pitch between successive turns, so as to reduce cross-modulation and to enable the device to be used efficiently with well-known automatic volume control circuits.

While Fig. 2 shows a system for receiving signals, it will be understood from the foregoing description that the invention is not limited to receiving, but may be used for transmission. For

example, the triode section may be arranged to generate sustained oscillations of a suitable carrier frequency and the signal variations representing speech, telegraph or the like, may be impressed on the signal input circuit and control grid 5, resulting in the production in the output circuit of a correspondingly modulated carrier wave which may be radiated or otherwise transmitted. It will also be understood that the invention is not limited to any particular frequency range. Thus the device I may be used for producing audio frequency beat notes, intermediate frequency waves, or high frequency waves, as desired.

Referring to Fig. 2, a description will now be given of a preferred structure embodying the electrode arrangement of Fig. 1. In Fig. 2, parts corresponding to similar parts of Fig. 1 bear the same designation numerals. Thus the numeral indicates an evacuated envelope of glass or other suitable material, having a re-entrant stem portion 32 terminating in a press 33.

Sealed into press 33 are the various lead-in and. electrode support wires 34: and 44, inclusive. Wires 34 and 44 support the tubular anode 8 which may be a circular or flattened cylinder. Similarly, wires 35 and 43 support the tubular anode |0 preferably coaxially with, but in spaced relation to, the lower edge of anode 8. Wires 36 and 42 support the grid l which, as shown, is in the form of a wire helically wound around and fastened to said wires. 36 and. 42. Wires 3'! and 4| support grid 6 within grid l which, as shown, is in the form of a wire helically wound around and fas ened to said wires 31 and 4|. Mounted posts 45 and 46.

within the grid 6 is the'control grid 5 also in the form of a wire wound around a pair of metallic Grid 5 instead of being supported directly from press 33 by-wires similar to wires 35: and 44, is supported on an insulator disc 4? which in turn is supported by a metal ring 48 fastened to the wires 36 and 42. As shown, the mica disc 47 is provided with perforations through which pass the wires 37, 4| and the grid support wires Q5 and 45. The lower end of wires 45 and 46 may be provided with beads or lugs 49 to prevent the grid from falling. Mounted concentrically within grid 5 is the cathode sleeve 3 which is provided on its exterior with the usual electronemitting coating 2. The sleeve and coating are supported by means of wire 38, while the heater filament 4 is fastened to the wires 39 and 40. Surrounding the anode 8 is a cylindrical mesh grid 9 which is supported from wires 31 and 4|, as shown. For the purpose of maintaining all the electrodes properly spaced there is provided a disc 50 of mica or other similar insulating material. Said disc is provided with suitable perforations to receive the upper ends of the wires 34, 36, 31, 45, 46, 4!, 42 and 44, as well as with a central perforation to receive the upper end of the cathode sleeve. This disc may be held in place by suitable beads or lugs (not shown) on the various wires. Disc 59 is preferably provided with extensions or lugs 5| adapted to engage the inner wall of the dome-shaped portion 52 of the tube envelope. Fastened to the grid 9 is a metallic cup-shaped cap 53 which in turn is fastened to the wires 36 and 42 which support grid 1. The cap 53 is arranged so as to clear the upper ends of the wires 34, 31, 45, 45, 4! and 44.

interposed between anodes 8 and I is the annular disc i! of mica or other similar insulating material supported by means of beads or lugs on the wires 34 and 44. As will be seen, the grid electrodes l and 6 are substantially coextensive in length with cathode 2, while the grid terminates just above the disc I I and, similarly, the outer shield grid 9 terminates just below the anode 8. As described above in connection with Fig.1, the cathode 2 may be considered as divided into an upper portion and a lower portion. The upper portion cooperates with electrodes 5. l 8, 9 to provide a pentode unit, while the lower portion cooperates with electrodes 6, I and. it to provide a space-discharge triode. It will also be noted that the electrodes 6 and 1 are common to both the pentode and triode sections, for the purposes described in connection with Fig. 1. Suitable connecting wires 54 to Bil are provided for the various electrodes, the control grid 5 being preferably connected by wire 61 to the usual metal cap 64.

It will be understood, of course, that the invention is not limited to a tube wherein the grid 6 is extended to act as a space charge grid for the triode section. For example, the grid 6 may terminate just above the disc I I so as to be substantially coextensive with grid 5, if desired. Accordingly, various changes and modifications may be made in the structure described without departing from the spirit and scope of the invention. For example, if desired the cathode instead of being a single unipotential cathode, may be of the type disclosed in Patent No. 2,049,164, whereone portion is an indirectly heated emitter and other portion is a filamentary or directly heated emitter. The term control grid as employed in this specification and in the claims is intended to cover a grid upon which variable potentials such as signal potentials are impressed, as

distinguished from a grid upon which a steady potential is impressed as is the case with the usual shield grid and the usual suppressor grid. The term space charge grid is intended to cover a grid which acts to neutralize the space charging eifect of the electrons from the cathode in the well known manner.

What I claim is:

1. A space discharge tube comprising an envelope having a pentode unit and a tetrode unit both said units having a common grid to act as the pentode suppressor grid and also as the tetrode accelerating grid.

2. In combination a pentode unit having a shield grid, a tetrode unit having a control grid and an accelerating grid and a unipotential connection from the shield grid of the pentode to the accelerating grid of the tetrode unit.

3. In combination a pair of anodes, means for emitting electrons to said anodes, a control grid effective to control only the stream between said emitting means and one of said anodes, and a single foraminous member positioned in the electron streams between said emitting means and both said anodes so as to exercise control over the electron streams from the said emitting means to both said anodes.

4. A tube of the oscillator-modulator type comprising a modulating section having an electron emitting cathode, an anode, a control grid, a

shield grid, a suppressor grid, an oscillator section comprising an anode spaced apart from the first mentioned anode, the shield grid of the modulator section being extended to form an accelerating grid for the oscillator section, and the suppressor grid of the modulator section being extended to form a control grid for the oscillator section.

5. A tube of the oscillator-modulator type comprising a modulator section having an electron emitting cathode, an anode for said cathode, a signal control grid, a suppressor grid, inner and outer shields for said anode, an oscillator section having an anode spaced from the first mentioned anode, the said inner shield of the modulator section being extended to form an accelerating grid for said oscillator section.

6. A tube of the oscillator-modulator type comprising a modulator section having an electron emitting cathode, an anode for said cathode, a signal control grid, a suppressor grid, and an oscillator section having an anode spaced from the first mentioned anode, the said suppressor grid being extended to form a control grid for the oscillator section.

7. A tube according to claim 5 in which the electron emitting cathode is common to both the modulator section and to the oscillator section.

8. A tube according to claim 6 in which the electron emitting cathode is common to both the modulator section and to the oscillator section.

9. A tube according to claim 5 in which the suppressor grid is extended to form a control grid for the oscillator section and the inner shield is extended to form a space-charge grid for the oscillator section.

10. A space discharge tube comprising an enclosing envelope containing a shield-grid unit having a control grid, and a tetrode unit having a control grid and an electrode which-is common to both units and arranged to act as the shield grid for the first-mentioned unit and as an accelerating grid for the second-mentioned unit.

11. A space discharge tube comprising anenclosing envelope containing a shield-grid unit,

and a tetrode unit having a control grid, said units having at least two. electrodes in common, one

of said common electrodes being a shield-grid for one unit and an accelerating grid for the other unit.

EMME'IT FINLEY CARTER. 

